Various types of mechanical stepless speed change apparatus have been provided. Automobiles, which are a typical machine requiring frequent speed change, have been provided with a so-called Van Dona type stepless speed change apparatus which combines steel belts and segment pieces to transmit rotary force between variable-gap V-pulleys, and a second type of stepless speed change apparatus which provides a stepless speed change in the bypass circuit of a differential gear mechanism.
Automobiles are often driven under severe conditions such as quick start and quick acceleration. As a result, the life of the power transmission system tends to be reduced.
In the case of the Van Dona type apparatus, the steel belts tend to have a short life. Furthermore, when a compact design is required, the highest output of the apparatus is generally said to be limited to about 100 horsepower.
In the case of the second type of apparatus, if the conventional stepless speed change device is used with friction wheels, it is also difficult to develop large horsepower because of the small area of frictional engagement.